Long Term Evolution (LTE) systems support two work modes: Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD).
FIG. 1 is a schematic diagram illustrating a frame structure in a TDD system according to the related art.
Referring to FIG. 1, the length of each radio frame 110 is 10 ms and the radio frame 110 is divided into two half-frames 120 with the length of 5 ms each. Each half-frame 120 includes eight time slots 130 and three special fields 140. The length of each time slot 130 is 0.5 ms. The special fields 140 include a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS). The total length of the DwPTS, GP, and UpPTS is 1 ms. Each subframe 135 consists of two continuous time slots, that is, the Kth subframe may consist of a time slot 2k and a continuous time slot 2k+1.
The TDD system supports 7 TDD uplink-downlink configurations, as shown in Table 1. Herein, D indicates a downlink subframe, U indicates an uplink subframe, and S indicates a special subframe including the above three special fields.
TABLE 1Config-urationswitchingsubframe numbernumberpoint cycle01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD
For the purpose of improving transmission rate of users, an LTE-Advanced (LTE-A) system is provided. In the LTE-A system, a larger work bandwidth is obtained by aggregating multiple Component Carriers (CCs), i.e. uplink-downlink links of a communication system are configured via Carrier Aggregation (CA), so as to support higher transmission rates. For example, in order to support a bandwidth of 100 MHz, five CCs of 20 MHz may be aggregated. Herein, each CC is called a cell. A Base Station (BS) can configure one User Equipment (UE) to work in multiple CCs, one of which is a Primary Cell (PCC or Pcell), and others are Secondary Cells (SCCs or Scells).
FIG. 2 is a schematic diagram illustrating conventional TDD uplink-downlink configuration of each CC in the same CA according to the related art.
Referring to FIG. 2, it is defined in the LTE-A TDD system that multiple aggregated CCs use the same uplink-downlink configuration. The CA shown in FIG. 2 includes two CCs which are PCC and SCC respectively. Each of the CCs uses the same uplink-downlink configuration. In this example, subframes 0, 1, 3˜6, 8 and 9 are configured as downlink subframes, subframes 2 and 7 are configured as uplink subframes.
For data received from the downlink subframe, the UE needs to perform positive acknowledgment or negative acknowledgment by sending ACK or NACK to the base station via the uplink subframe. Thus, several downlink subframes are configured into a Hybrid Automatic Repeat Request acknowledgement (HARQ-ACK) bundling window, and the HARQ-ACK feedback information of each downlink subframe in the same HARQ-ACK bundling window is sent via the same uplink subframe.
Referring to FIG. 2, subframes 4, 5, 6, and 8 of a radio frame n shown by slash lines belong to a HARQ-ACK bundling window, and the HARQ-ACK feedback information of each subframe in the HARQ-ACK bundling window will be sent via a subframe 2 of a radio frame n+1. The content “N” in the box corresponding to each subframe indicates: the HARQ-ACK feedback information of this subframe is sent via the N-th subframe from this subframe. For example, the content in the box corresponding to the subframe 4 is 8, and the eighth subframe from the subframe 4 is the subframe 2 in the radio frame n+1, thus the HARQ-ACK feedback information of the subframe 4 is sent via the subframe 2 in the radio frame n+1; for another example, the content in the box corresponding to the subframe 8 is 4, and the fourth subframe from the subframe 8 is also the subframe 2 in the radio frame n+1, thus the HARQ-ACK feedback information of the subframe 8 in radio frame n is sent via the subframe 2 in radio frame n+1.
One mode of sending the HARQ-ACK feedback information by the UE is a Physical Uplink Control Channel (PUCCH) format 3, and the PUCCH format 3 supports 5 CCs at most. The base station sends an Uplink (UL) grant via a Physical Downlink Control Channel (PDCCH), and schedules Physical Uplink Shared Channel (PUSCH) resources for the UE. The value of UL Downlink Assignment Index (DAI) in the UL grant is used to determine the number of bits used when the HARQ-ACK feedback information is transmitted via the PUCCH format 3.
It is supposed that the UE is configured with 2 CCs, the value of the UL DAI is M, and FIG. 2 is taken as an example. In this case, if a work mode of the CC is Single Input Multiple Output (SIMO), the number of bits needed by the HARQ-ACK feedback information is M; if a work mode of the CC is Multiple Input Multiple Output (MIMO), if the total number of bits of the HARQ-ACK feedback information of all CCs to be transmitted by the UE is less than or equal to N (e.g. 20), the number of bits needed by the HARQ-ACK feedback information of this CC is M*2; if a work mode of the CC is MIMO, if the total number of bits of the HARQ-ACK feedback information of all CCs to be transmitted by the UE is larger than N (e.g. 20), the number of bits needed by the HARQ-ACK feedback information of this CC is M.
Actually, when frequency domain distance between multiple CCs performing the CA is long enough, the CCs may use different TDD uplink-downlink (U-D) configurations without bringing any interference between each other. In addition, in some case, phase frequencies of different CCs may be deployed with different U-D configurations (e.g. the adjacent frequencies are configured with different Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) configurations). If the same uplink-downlink configuration is used for these CCs, serious adjacent channel interference can be caused. Therefore, in subsequent research of LTE-A, an important subject is how to effectively support the case that the TDD uplink-downlink configurations of the multiple CCs of the CA are different. For example, when the TDD uplink-downlink configurations of the multiple CCs of the CA are different, how to determine the number of bits used for transmitting the HARQ-ACK feedback information in the PUSCH is a technical problem to be solved.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.